In the related art, liquid immersion cooling is known as a method of cooling a server, which is an electronic circuitry including a heat generating circuit. Liquid immersion cooling is a technique in which a coolant container (hereinafter, referred to as a liquid immersion tank) is filled with a liquid coolant that has electrical insulation and is inert (hereinafter referred to as an “inert coolant”) so that the entire server is immersed, and the inert coolant is forcibly circulated using, for example, a pump so that cooling is performed via heat transfer between the server and the inert coolant. As the inert coolant, for example, fluorocarbon (e.g., Fluorinert (registered trademark) manufactured by 3M Company) is adopted, and heat of the server, which is absorbed by the inert coolant, is discharged to the outside of the liquid immersion tank, and is dissipated via an air regulation device or a cooling tower (chiller) at the outside.
FIG. 1A illustrates the structure of a liquid immersion cooling system 10 according to a comparative technique. The liquid immersion cooling system 10 uses an inert coolant L as a coolant of a cooling device 20, which cools an electronic circuitry E by circulating the coolant in a liquid immersion tank 3. The inert coolant L is formed so as to be cooled by another coolant W at the outside of the liquid immersion tank 3. Here, the other coolant is referred to as a first coolant, and the coolant circulated in the liquid immersion tank 3 is referred to as a second coolant. Cooling water is generally used as the first coolant. That is, the liquid immersion cooling system 10 is a system that cools the electronic circuitry E, which includes a heat generating circuit, in an active state (operating state) within the liquid immersion tank 3 by the inert coolant L as the second coolant, which is cooled by the cooling water W as the first coolant. The liquid immersion cooling system 10 includes a chiller 1, which is called a chiller or a cooling tower that cools the cooling water W, a heat exchanger 2 that cools the inert coolant L by performing heat exchange between the cooling water W and the inert coolant L, the liquid immersion tank 3 that accommodates and cools the electronic circuitry E, and a lid 4 that opens and closes an opening 3A in the liquid immersion tank 3.
There are a pipe P1, through which the cooling water W is circulated, between the chiller 1 and the heat exchanger 2 and a pipe P2, through which the inert coolant L is circulated, between the heat exchanger 2 and the liquid immersion tank 3. A pump P is provided in the pipe P2 to forcibly circulate the inert coolant L. The electronic circuitry E, which is cooled by the inert coolant L in the liquid immersion tank 3, is, for example, a server or a storage. A space SP between a liquid level LL of the inert coolant L in the liquid immersion tank 3 of the inert coolant L and the lid 4 is filled with a coolant vapor VL that has evaporated from the liquid level LL of the inert coolant L. In addition, a cable 5 is coupled to the electronic circuitry E, which is accommodated in the liquid immersion tank 3, to perform the supply of power or the transmission/reception of signals. The cable 5 is discharged to the outside of the liquid immersion tank 3 through a cable inlet 6, and is coupled to a control device (not illustrated).
Here, a fluorocarbon-based liquid coolant, which is used as the inert coolant L, evaporates when it is left to stand in the atmosphere. From the viewpoint of stable management of the liquid immersion cooling system, it is important to suppress the amount of coolant that is vaporized and diffused into the atmosphere, in order to suppress the management cost due to replenishment of an expensive fluorine-based coolant.
Related techniques are disclosed in, for example, Japanese Laid-Open Patent Publication Nos. 2010-226771, 10-318874, and 07-091788.